Skeletal muscle electrical stimulation improves baroreflex sensitivity ...

Autonomic Neuroscience: Basic and Clinical 193 (2015) 92–96

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Skeletal muscle electrical stimulation improves baroreflex sensitivity and heart rate variability in heart failure rats Ananda Lazzarotto Rucatti a, Rodrigo Boemo Jaenisch a, Douglas Dalcin Rossato a, Jéssica Hellen Poletto Bonetto a, Janaína Ferreira b, Leder Leal Xavier c, Anelise Sonza a, Pedro Dal Lago a,d,⁎ a

Physiology Laboratory, Universidade Federal de Ciências da Saúde de Porto Alegre — UFCSPA, Porto Alegre, RS, Brazil Instituto do Coração — InCor, Universidade de São Paulo, USP, São Paulo, Brazil Laboratório de Biologia Celular e Tecidual, PUCRS, Rio Grande do Sul, Brazil d Physical Therapy Department, UFCSPA, Porto Alegre, RS, Brazil b c

a r t i c l e

i n f o

Article history: Received 12 June 2015 Received in revised form 19 August 2015 Accepted 22 August 2015 Keywords: Heart failure Electrical stimulation Arterial baroreflex Cardiovascular autonomic Sympatho-vagal balance Heart rate parasympathetic modulation

a b s t r a c t The goal of the current study was to evaluate the effects of electrical stimulation (ES) on the arterial baroreflex sensitivity (BRS) and cardiovascular autonomic control in rats with chronic heart failure (CHF). Male Wistar rats were designated to one of four groups: placebo sham (P-Sham, n = 9), ES sham (ES-Sham, n = 9), placebo CHF (P-CHF, n = 9) or ES CHF (ES-CHF, n = 9). The ES was adjusted at a low frequency (30 Hz), duration of 250 μs, with hold and rest time of 8 s (4 weeks, 30 min/day, 5 times/week). It was applied on the gastrocnemius muscle with intensity to produce a visible muscle contraction. The rats assigned to the placebo groups performed the same procedures with the equipment turned off. The two-way ANOVA and the post hoc Student–Newman– Keuls tests (P b 0.05) were used to data comparison. The BRS was higher in ES-Sham group compared to the PSham group and the ES-CHF group compared to the P-CHF group. ES was able to decrease heart rate sympathovagal modulation and peripheral sympathetic modulation in ES-CHF compared to P-CHF group. Interestingly, heart rate sympatho-vagal modulation was similar between ES-CHF and P-Sham groups. Thus, ES enhances heart rate parasympathetic modulation on heart failure (ES-CHF) compared to placebo (P-CHF), with consequent decrease of sympatho-vagal balance in the ES-CHF group compared to the P-CHF. The results show that a 4 week ES protocol in CHF rats enhances arterial BRS and cardiovascular autonomic control. © 2015 Elsevier B.V. All rights reserved.

1. Introduction Chronic heart failure (CHF) is considered a clinical syndrome involving multiple organs that is developed by any functional or structural impairment of heart blood ejection or ventricular filling (Yancy et al., 2013). The CHF shows abnormalities of other systems, beyond the heart (Ventura-Clapier et al., 2002). In this syndrome, the sympathetic hyperactivity and the parasympathetic hypoactivity are characteristics of the neurohumoral excitation (Floras, 2009), which are connected with the baroreflex sensitivity (BRS) attenuation (La Rovere et al.,

Abbreviations: ES, Electrical stimulation; CHF, Chronic heart failure; BRS, Baroreflex sensitivity; MI, Myocardial infarction; MAP, Mean arterial pressure; HRV, Heart rate variability; BPV, Blood pressure variability; LF/HF, Sympatho-vagal balance; LV, Left ventricle; RV, Right ventricle; LVSP, LV systolic pressure; +dP/dtmax, LV maximum change in pressure over time; −dP/dtmax, LV minimum change in pressure over time; LVEDP, LV end-diastolic pressure; HW, Heart weight; BW, Body weight; SBP, Systolic arterial blood pressure; PI, Pulse interval. ⁎ Corresponding author at: Universidade Federal de Ciências da Saúde de Porto Alegre, Sarmento Leite, 245, 90050-170 Porto Alegre, RS, Brazil. E-mail address: [email protected] (P.D. Lago).

http://dx.doi.org/10.1016/j.autneu.2015.08.008 1566-0702/© 2015 Elsevier B.V. All rights reserved.

1998). Considering these circumstances, heart-rate variability (HRV) reduction and an impairment of short-term control of arterial pressure (AP) (La Rovere et al., 1998) have been related with an augmented risk of sudden death from cardiac cause (Schwartz and La Rovere, 1998). Skeletal muscles are involved in the CHF syndrome. Skeletal muscle myopathy (Mancini et al., 1992), muscle fiber atrophy (Drexler et al., 1992), reduction in muscle strength and in the cross-sectional area of skeletal striated muscle fibers (Buller et al., 1991) are predictors of exercise tolerance decrease in CHF patients. One of the recommendations as part of the treatment for CHF patients is the physical training (Working Group on Cardiac R, Exercice P and Working Group on Heart Failure of the European Society of C, 2001). However, some individuals do not adapt to the physical training and others are not able to support including low levels of exercise. Several studies show that exercise and muscle afferent activation can interfere in the arterial baroreflex in humans (Gademan et al., 2011; Scherrer et al., 1990) and animals (Hammond et al., 2000; Kim et al., 2005; Lima et al., 2015). The autonomic regulations are produced by both voluntary muscle activation and the central stimulation (Scherrer et al., 1990). At the same time, muscle metaboreflex is activated by the CHF syndrome during strenuous exercise (Hammond et al.,

A. Lazzarotto Rucatti et al. / Autonomic Neuroscience: Basic and Clinical 193 (2015) 92–96

2000) and consequently, sympathetic hyperactivity occurs. Transcutaneous electrical nerve stimulation (TENS) that is a muscle afferent stimulus was applied in CHF patients, an increase in BRS was found (Gademan et al., 2011) and this modulates sympathetic activity. The use of electro-acupuncture has shown in CHF rats, similar results (Lima et al., 2015). Functional electrical stimulation (FES) a modality of ES that causes muscle contraction has shown promising beneficial effects in CHF patients, such as increase in oxidative enzyme levels, skeletal striated muscle mass (type I fibers), prevention of muscle atrophy (Nuhr et al., 2004), peak VO2 (Dobsak et al., 2006a), endothelial function and emotional status improvement (Karavidas et al., 2013). Both therapies suggest to be alternative treatments for the CHF subjects who cannot adapt to the conventional exercise training programs (Gademan et al., 2011; Smarta et al., 2013). Nevertheless, the effect of ES on neurohumoral control of the cardiovascular system in CHF rats has not been evaluated. Therefore, this study was conducted to test the hypothesis that a 4-week protocol of electrical stimulation could be associated with improvement in baroreflex sensitivity and heart rate variability in rats with CHF. 2. Material and methods 2.1. Animals Thirty-six male Wistar rats (230 to 280 g) from the Animal Breeding Unit of the Universidade Federal de Ciências da Saúde de Porto Alegre (UFCSPA) were used for the experiments. The animals received food and water ad libitum and they were housed two per cage in an animal room kept at 22 °C under a 12:12-h light–dark cycle. The experiment followed the ethical procedures established by the Guide for Care and Use of Experimental Animals, number 85-23, revised in 1996, published by the National Institutes of Health. All procedures from this study were approved by the Ethics and Research Committee from UFCSPA (protocol 006/10). 2.2. Surgery to induce myocardial infarction (MI) To induce MI, rats were intubated and artificially ventilated after being anesthetized with xylazine (12 mg/kg ip) and ketamine (90 mg/kg ip). As previously described (Pfeffer et al., 1979), the left coronary artery ligation and the sham surgeries were carried out. To prevent pain and infection after operation, a single dose of monofenew (0.05 ml/100 g) and gentamicin (0.05 ml/100 g) were administered. 2.3. Experimental design The time for the CHF animals to recover and to develop the CHF state following MI surgery was 6 weeks (Pfeffer et al., 1979). The sham groups had the same time period to recover. Five weeks after the operation, the sham rats were randomly designated into one of the following groups: placebo sham rats (P-Sham, n = 9) or ES sham rats (ES-Sham, n = 9); and the CHF animals were randomly assigned into one of the groups: placebo CHF rats (P-CHF, n = 9) or ES CHF rats (ES-CHF, n = 9). 2.4. Electrical stimulation protocol The adaption protocol to the electrical stimulation started on the 5th week after the surgery and included 5 min on first day and accrued 5 min per day until completing 5 days. The ES protocol began in the 6th week. It comprised 30 min/day, 5 days/week for 4 weeks. The right leg of each rat was shaved and they laid on a platform with its right knee extended. During the ES, the animals were kept awake in a device built in our laboratory that mimics a burrow (Lima et al., 2015) and allows a comfortable positioning. The electrical stimulator (FES VIF 995, Quark, Piracicaba, Brazil) was applied on the gastrocnemius

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muscle of the right leg with a surface electrode (7.5 mm × 7.5 mm). The current was symmetric biphasic adjusted at a low frequency (30 Hz), duration of 250 μs, with hold and rest time of 8 s, with necessary intensity to produce a visible muscle contraction without causing any apparent discomfort (de Leon et al., 2011). The rats from the placebo groups performed the same procedures with the equipment turned off. 2.5. Awake measurements of cardiovascular parameters Under general anesthesia as above described, in the week after the ES protocol, two catheters filled with saline (0.06 ml) and heparin (0.01 ml) were implanted into the abdominal aorta and inferior vena cava, which were used to measure mean arterial pressure (MAP) and drugs administration, respectively. Conscious rats were studied on the subsequent day after the catheter placement (Jaenisch et al., 2011; Quagliotto et al., 2008). The arterial catheter was connected to a 40 cm tube attached to a strain-gauge pressure transducer (Miniature Pulse Transducer RP-155, Houston, USA), coupled to a pressure amplifier (General Purpose Amplifier 4 — model 2, Stemtech Inc., Houston, USA), and blood-pressure signals were recorded over a 15-min period, 1 kHz sampling frequency (Windaq — AT/CODAS, Dataq Instruments Inc., Akron, USA). On a beat-to-beat basis the measured data were analyzed to quantify the variables of interest (Jaenisch et al., 2011; Quagliotto et al., 2008). 2.6. Baroreflex sensitivity On the subsequent day following the catheter placement, MAP and HR were registered for 15 min as baseline control. HR changes to test BRS were recorded during peak changes (augment or reduction) in MAP due to a single dose of venous injection of phenylephrine (8 μg/ml; Sigma Chemical, St. Louis, USA) or sodium nitroprusside (100 μg/ml; Sigma Chemical), respectively (Jaenisch et al., 2011; Quagliotto et al., 2008). The alterations in MAP were within the 10 to 30 mm Hg range and the BRS determination was made by fitting the MAP and HR alterations to a sigmoidal logistic equation (Head and McCarty, 1987). 2.7. Cardiovascular autonomic control Spectral analysis of systolic arterial blood pressure (SBP) and pulse interval (PI) to evaluate the sympathetic and parasympathetic cardiovascular modulation was performed by an autoregressive method. From the original recordings, samples were exported to create a database for the analysis, according to the HRV guidelines (Guidelines, 1996). Succinctly, continuous series of PI (tachogram) were supplied by a derivative-threshold algorithm. The systogram was created through the beat-to-beat SBP derived from BP signals. The “low frequency” (LF, 0.2–0.75 Hz) and “high frequency” (HF, 0.75–3.0 Hz) spectral components of PI and SBP were explicit in absolute values (ms2 and mm Hg, respectively) and in normalized units (n.u.). The n.u. were obtained after calculate the relation between the power of either LF or HF components divided by the total power subtracted of the power of the very low frequency component (frequencies ≤ 0.2 Hz). The result is then multiplied by 100. 2.8. Cardiac hemodynamic evaluation In the subsequent day (24 h) following the autonomic evaluation, the animals were anesthetized, as above described, for cardiac hemodynamic evaluation. For that, a catheter (PE-50) was introduced into the right carotid artery and during a 5-min period the AP was registered. Later, the catheter was placed inside the left ventricle (LV) and the standard graphic recordings of ventricular pressure were used to monitor the pulse wave and registered for 5 min, following the protocol

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suggested by Jaenisch et al. (2011). These records were used to extract LV systolic pressure (LVSP), LV maximum change in pressure over time (+ dP/dtmax), LV minimum change in pressure over time (− dP/dtmax) and LV end-diastolic pressure (LVEDP) (Jaenisch et al., 2011). 2.9. Morphological characteristics, pulmonary and hepatic congestion All animals were sacrificed by anesthetic overdose (Thiopental 80 mg/kg ip). The heart was removed and weighed; thereafter, the right ventricle (RV) and LV were dissected and weighed to determine the heart weight to body weight ratio (HW/BW), LV/BW and RV/BW ratios. Lungs and liver were removed and weighted before and after being dehydrated (for 48 h at 80°) to determine pulmonary and hepatic congestion. The calculation of the infarction area was made by planimetry, and for that, the LV was filled with an insufflating latex balloon and submerged in formaldehyde for 24 h preceding the analysis (Lindpaintner et al., 1993). 2.10. Morphological measurements of skeletal muscle Digitized images of the muscle sections were obtained using a microscope (Olympus BX 50, USA) (20 ×) coupled to a video camera (Moticam 2500, China) interfaced by Motic Images Plus 2.0 software. The measurements from the acquired images were calculated through the Image Pro Plus Software (Image Pro-Plus 6.1; Media Cybernetics, USA) and at least 9 images were analyzed in each muscle per animal. Muscle fiber area was estimated using a point counting technique (Hermel et al., 2006; Ilha et al., 2008). Grid masks with a point value of 224 μm2 were laid over the images and the area of the muscle fiber was calculated using the equation as follows: Â = ∑p ∙ a/p, where Â is the area, ∑ p is the sum of the counted points and a/p is the area/ point value. Blood vessels densities were estimated counting the total number of vessels in the muscle section. 2.11. Statistics The collected data were shown as mean ± standard deviation (SD). A two-way ANOVA followed by Student Newman Keuls post-hoc tests were used to compare the group (CHF or Sham) and intervention (ES or P) effects (P b 0.05). For data analysis, the Sigma Plot 12.0 for Windows (Systat Software, Chicago, USA) was used. 3. Results 3.1. Mortality, morphological characteristics, pulmonary and hepatic congestion The mortality, during or after the MI-induced surgery, in rats with CHF was 35%. No deaths happened during the study for the sham groups. Table 1 shows that the HW/BW, LV/BW and RV/BW were higher in the CHF groups than Sham groups (F(3,32) = 21.904; P b 0.001,

F(3,32) = 6.645; P b 0.015 and F(3,32) = 6.525; P = 0.016, respectively). No differences were found for pulmonary and hepatic congestion. There were no behavioral changes associated with stress or adverse effects in rats that participated in the ES protocol. 3.2. Baroreflex sensitivity The values found to the baroreceptor-mediated reflex demonstrated that the highest slope point of the MAP (MAP50) were lower in the CHF groups than Sham groups (F(3,30) = 19.938; P b 0.001). BRS (gain) was higher in the ES-Sham group than P-Sham group (F(3,30) = 10.865; P = 0.003). The ES-CHF group showed a significant increase in the BRS compared with the P-CHF (F(3,30) = 10.865; P = 0.022) and P-Sham group (F(3,30) = 10.865; P = 0.002). These data are summarized in Table 2. 3.3. Cardiovascular autonomic control There was lower heart rate that might be related to lower sympathetic and higher vagal modulation in ES-CHF than P-CHF group [LF (n.u.): 25.6 ± 3.9 vs. 38.4 ± 7.6, P = 0.05] and peripheral sympathetic modulation (LF: 2.2 ± 0.9 vs. 6.5 ± 1.6 ms2, P = 0.005) for the same groups. Furthermore, heart rate sympatho-vagal modulation was similar between ES-CHF and P-Sham groups (LF: 25.6 ± 3.9 vs. 28 ± 8.6 ms2, P = 0.6). Thus, ES showed higher heart rate parasympathetic modulation in heart failure animals than to placebo with CHF [HF (n.u.): 74.4 ± 4.3 vs. 61.6 ± 8.3, P = 0.04], with consequent sympatho-vagal balance (0.3 ± 0.1 vs. 0.6 ± 0.2, P = 0.03). Heart rate variability (HRV) was lower in both heart failure groups in relation to sham groups. Blood pressure variability (BPV) and HRV components are presented in Table 3. 3.4. Hemodynamics variables LVEDP was increased in the CHF groups (F(3,20) = 28.313; P b 0.001) than sham groups. LVSP (F(3,32) = 5.025; P = 0.032), + dP/dtmax (F(3,32) = 10.213; P = 0.003) and − dP/dtmax (F(3,32) = 26.587; P b 0.001) values were decreased when compared to sham groups (Table 4). 3.5. Skeletal muscle morphological parameters There were no differences between groups in relation to crosssectional area of muscle fiber (μm2) (P-Sham = 1279 ± 142 μm2; ESSham = 1267 ± 137 μm2; P-CHF = 1215 ± 151 μm2; ES-CHF = 1434 ± 354 μm2) (F(3,20) = 0.00000827; P = 0.462 for group, F(3,20) = 0.368; P = 0.551 for intervention, F(3,20) = 0.563; P = 0.462 for interaction) or blood vessels densities (number of blood vessels/ muscle cross section) (P-Sham = 81.3 ± 12.4; ES-Sham = 74.8 ± 20.6; P-CHF = 77.2 ± 20.3; ES-CHF = 84.8 ± 24.6) (F(3,20) = 0.106; P = 0.748 for group, F(3,20) = 0.00426; P = 0.949 for intervention, F(3,20) = 0.628; P = 0.437 for interaction).

Table 1 Body weight, morphometric cardiac characteristics, infarct area and lung and hepatic congestion of sham-operated rats and rats with left ventricular dysfunction. Groups

Initial BW (g)

Final BW (g)

Infarcted area (%)

HW/BW (mg/g)

LV/BW (mg/g)

RV/BW (mg/g)

Pulmonary congestion (%)

Hepatic congestion (%)

P-Sham ES-Sham P-CHF ES-CHF

244.8 ± 19 244.9 ± 23 244.2 ± 11 237.4 ± 9

348.3 ± 34 329.3 ± 42 328.8 ± 23 324.2 ± 15

– – 24.84 ± 6.9 25.37 ± 6.2

2.8 ± 0.3 3.0 ± 0.4 3.4 ± 0.3⁎ 3.5 ± 0.2⁎

2.3 ± 0.2 2.4 ± 0.4 2.6 ± 0.2 2.7 ± 0.3⁎

0.4 ± 0.1 0.6 ± 0.3 0.8 ± 0.2⁎⁎ 0.7 ± 0.3⁎⁎

74.3 ± 5.5 70.7 ± 4.4 73.0 ± 3.1 71.4 ± 4.6

74.0 ± 3.1 73.9 ± 2.4 73.5 ± 0.8 71.3 ± 3.9

Values are means ± SD; n = 9 for all groups. BW, body weight; HW/BW, heart weight-to-BW ratio; LV/BW, left ventricle-to-BW ratio and RV/BW, right ventricle-to-BW ratio; P-Sham, placebo sham rats; ES-Sham, electrical stimulation sham rats; P-CHF, placebo heart failure rats; ES-CHF, electrical stimulation heart failure rats. ⁎ P b 0.05 compared with P-Sham and ES-Sham. ⁎⁎ P b 0.05 compared with P-Sham.

A. Lazzarotto Rucatti et al. / Autonomic Neuroscience: Basic and Clinical 193 (2015) 92–96 Table 2 Baroreceptor reflex responses of HR sham-operated rats and rats with left ventricular dysfunction. Groups

MAP50 (mm Hg)

Maximum gain (beats min−1 mm Hg−1)


107.6 ± 10.6 108.5 ± 6.2 97.5 ± 8.0⁎⁎ 94.01 ± 6.0⁎⁎

−5.28 ± 2.3 −9.3 ± 5.6⁎ −6.9 ± 2.9 −11.5 ± 3.5⁎⁎⁎

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Table 4 Hemodynamics variables of sham-operated rats and rats with left ventricular dysfunction. Groups

LVEDP (mm Hg)

LVSP (mm Hg)

+dP/dtmax (mm Hg/s)

−dP/dtmax (mm Hg/s)


4.2 ± 1.3 4.2 ± 0.8 8.8 ± 4.0⁎ 13.1 ± 6.2⁎

123.1 ± 16.5 111.4 ± 18.6 104.6 ± 13.9⁎⁎ 106.3 ± 13.6⁎⁎

6900 ± 1347 6043 ± 1667 5332 ± 797⁎⁎ 5123 ± 469⁎⁎

5451 ± 1076 4406 ± 834 3645 ± 520⁎ 3635 ± 350⁎

Values are means ± SD; n = 9 for all groups. HR, heart rate; and MAP50, values related to the highest slope point of the mean arterial pressure. ⁎ P b 0.05 compared with P-Sham. ⁎⁎ P b 0.05 compared with P-Sham and ES-Sham. ⁎⁎⁎ P b 0.05 compared with P-CHF and P-Sham.

Values are means ± SD; n = 9 for all groups. LVEDP, left ventricular end-diastolic pressure; LVSP, left ventricular systolic pressure; +dP/dtmax, left ventricular maximum change in pressure over time; −dP/dtmax, left ventricular minimum change in pressure over time. ⁎ P b 0.05 compared with P-Sham and ES-Sham. ⁎⁎ P b 0.05 compared with P-Sham.

4. Discussion

Treatment with ES in patients with CHF may be an alternative to the use of aerobic exercises for patients with CHF and especially for those who are unable to perform them. A meta-analysis of randomized controlled trials demonstrated that ES in patients with CHF produces a similar gain in the distance walked of the 6-min walk test and in the muscle strength when compared with aerobic exercise and an increase in the peak VO2 as compared with the control group (Sbruzzi et al., 2010). In a previous study with CHF rats (de Leon et al., 2011), after a 20 days protocol with ES, 50% higher content of GLUT-4 protein was found. Adding, the reduced vascular density and a raise in muscle weight, indicate an improvement in the cross-sectional area of muscle fibers in CHF rats (de Leon et al., 2011). Alterations in autonomic function occur in several interrelated cardiac conditions. Activation of the sympathetic nervous system (SNS) and inhibition of the parasympathetic system have long been recognized as manifestations of the clinical syndrome of CHF (Florea and Cohn, 2014). Therefore, sympathetic hyperactivity, vagal attenuation and BRS reduction were observed in this report and other (Schwartz and La Rovere, 1998); this lead to impaired HRV, which are related to alterations in the tissue perfusion and hemodynamic function. However, it has little knowledge in relation to autonomic alterations in CHF after use of ES. This study shows that ES increases BRS (gain) of 66% in CHF and 76% in Sham group compared to their controls. Furthermore, ES was able to reduce LF (n.u.) of 34% and LF of 133% in CHF rats. Interestingly, heart rate sympatho-vagal modulation was similar between ES-CHF and P-Sham groups. Thus, ES in rats with CHF was 20% higher of HF (n.u.) with a decrease of sympatho-vagal balance. The positive effects of exercise training in CHF are associated with neural control of the cardiovascular system. These effects, in CHF, include reduction of sympathetic outflow (Fraga et al., 2007), sympathetic toxicity of cardiac (Oliveira et al., 2009) and skeletal (Bacurau et al., 2009) muscles by exercise training. However, some individuals cannot tolerate levels of exercise by presenting a worsened physical state. Thus, the use of a protocol for muscle ES may be an alternative to conventional exercise training, based on the results of this study and others (de Leon et al., 2011; Dobsak et al., 2006b; Sbruzzi et al., 2010).

It has been demonstrated in the present study, to the best of our knowledge, that the ES in the peripheral muscles of rats with CHF induced the following: 1) an improvement in the arterial baroreceptor sensitivity, as demonstrated by the increase maximum gain (BRS); 2) a decrease of heart rate sympatho-vagal modulation (LF ms2 and LF n.u.); and 3) an increase in heart rate parasympathetic modulation (HF n.u.) and a decrease in sympatho-vagal balance (LF/HF). Interestingly, no differences were found comparing the ES-Sham to placebo groups in these parameters. The reason for that may be explained because in the Sham groups there were no alterations in the studied variables. In addition, the duration of protocol period of ES may have not been sufficient to produce benefits in normal rats. Several parameters were evaluated to determine the severity of left ventricular dysfunction after the MI. The LVEDP, was approximately two times higher in animals of CHF groups when compared to the Sham groups. This increase in LVEDP characterizes the development of a slight to moderate CHF (Pfeffer et al., 1979). The area of MI was found to be approximately 25% of the total area of LV in CHF groups. Due to the slight degree of pathology, possibly may not have been a decrease in vessel density in skeletal muscle, but a change in blood–tissue support for left ventricular dysfunction, possibly adjusted for the improvement of the baroreflex (gain) and sympatovagal modulation, as suggested by these findings. One of the beneficial effects of ES is associated to enhance morphological changes in skeletal muscles (de Leon et al., 2011). Moreover, metabolic adaptations in CHF patients submitted to an ES protocol suggest an aerobic metabolism improvement (Nuhr et al., 2004). Novel researches have been published about the successful use of the ES in rehabilitation of patients with CHF (Banerjee et al., 2009; Karavidas et al., 2013). ES enhances functional capacity, quality of life, emotional condition (Jaenisch et al., 2011), skeletal muscle blood supply and power (Dobsak et al., 2006b). However, there is no agreement related to the responses of ES in the physiopathology of CHF. The present report shows that ES has promising beneficial effects on arterial baroreceptor sensitivity and improvement in the autonomic function in CHF rats.

Table 3 Heart rate variability and blood pressure variability responses to electrical stimulation of sham-operated rats and rats with left ventricular dysfunction. Groups


Heart rate components

Blood pressure components

HRV (ms2)

LF (ms2)

HF (ms2)

LF (n.u.)

HF (n.u.)

LF/HF

BPV (mm Hg2)

LF (mm Hg2)

92.8 ± 61.1 108.9 ± 62.5 58.3 ± 17.9⁎ 64.2 ± 18⁎

5.1 ± 2.6 4.5 ± 2.1 6.1 ± 1 3.9 ± 1.1⁎⁎

12.7 ± 3.4 8.4 ± 1.7 10.5 ± 4.9 11.6 ± 3.2

28 ± 8.6 33.7 ± 5 38.4 ± 7.6 25.6 ± 3.9⁎⁎

71.9 ± 8.6 66.3 ± 5 61.6 ± 8.3 74.4 ± 4.3⁎⁎

0.4 ± 0.2 0.5 ± 0.1 0.6 ± 0.2 0.3 ± 0.1⁎⁎

32.8 ± 17.6 38.5 ± 22.2 27.8 ± 10.2 14.8 ± 19.9

5.5 ± 2.3 9.3 ± 4.6 6.5 ± 1.6 2.2 ± 0.9⁎⁎

Values are means ± SD; n = 9 for all groups. HRV: heart rate variability; LF: low frequency component; HF: high frequency component; LF/HF: sympatho-vagal balance; BPV: blood pressure variability. ⁎ P b 0.05 compared with P-Sham and ES-Sham. ⁎⁎ P ≤ 0.05 compared with P-HF.

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A limitation of this study was not carried out the direct evaluation of vagal and sympathetic tone. This analysis could elucidate the decrease in sympathetic activity, which is elevated in this disease, and the increase of vagal tone, with consequent improvement of the gain of the complex BRS through the protocol of muscle ES. Another aspect is related to BRS and cardiovascular measurements made ~24 h after anesthesia. The recover from anesthesia could influence the studied parameters, nevertheless, all groups were submitted to the same procedure and consequently they were evaluated under the same conditions. These findings suggest the contribution for using ES as an additional intervention in CHF patients without the use of medicine. Possible beneficial effects of ES in humans may be expected as an alternative treatment for clinical changes in autonomic nervous system in CHF patients. The convenience of applying the technique and the low costs should be considered as well. Additionally, clinical studies are important to be done to verify the effects of ES on other variables in CHF patients. Acknowledgments We gratefully acknowledge the support from the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul (FAPERGS) and UFCSPA, Brazil. References Bacurau, A.V., Jardim, M.A., Ferreira, J.C., Bechara, L.R., Bueno Jr., C.R., Alba-Loureiro, T.C., Negrao, C.E., Casarini, D.E., Curi, R., Ramires, P.R., Moriscot, A.S., Brum, P.C., 2009. Sympathetic hyperactivity differentially affects skeletal muscle mass in developing heart failure: role of exercise training. J. Appl. Physiol. 106, 1631–1640. Banerjee, P., Caulfield, B., Crowe, L., L. CA, 2009. Prolonged electrical muscle stimulation exercise improves strength, peak VO2, and exercise capacity in patients with stable chronic heart failure. J. Card. Fail. 15, 319–326. Buller, N.P., Jones, D., Poole-Wilson, P.A., 1991. Direct measurement of skeletal muscle fatigue in patients with chronic heart failure. Br. Heart J. 65, 20–24. de Leon, E.B., Bortoluzzi, A., Rucatti, A., Nunes, R.B., Saur, L., Rodrigues, M., Oliveira, U., Alves-Wagner, A.B., Xavier, L.L., Machado, U.F., Schaan, B.D., Dall'Ago, P., 2011. Neuromuscular electrical stimulation improves GLUT-4 and morphological characteristics of skeletal muscle in rats with heart failure. Acta Physiol. 201, 265–273. Dobsak, P., Novakova, M., Fiser, B., Siegelova, J., Balcarkova, P., Spinarova, L., Vitovec, J., Minami, N., Nagasaka, M., Kohzuki, M., Yambe, T., Imachi, K., Nitta, S., Eicher, J.C., Wolf, J.E., 2006a. Electrical stimulation of skeletal muscles. An alternative to aerobic exercise training in patients with chronic heart failure? Int. Heart J. 47, 441–453. Dobsak, P., Novakova, M., Siegelova, J., Fiser, B., Vitovec, J., Nagasaka, M., Kohzuki, M., Yambe, T., Nitta, S., Eicher, J.C., Wolf, J.E., Imachi, K., 2006b. Low-frequency electrical stimulation increases muscle strength and improves blood supply in patients with chronic heart failure. Circ. J. 70, 75–82. Drexler, H., Riede, U., Munzel, T., Konig, H., Funke, E., Just, H., 1992. Alterations of skeletal muscle in chronic heart failure. Circulation 85, 1751–1759. Floras, J.S., 2009. Sympathetic nervous system activation in human heart failure: clinical implications of an updated model. J. Am. Coll. Cardiol. 54, 375–385. Florea, V.G., Cohn, J.N., 2014. The autonomic nervous system and heart failure. Circ. Res. 114, 1815–1826. Fraga, R., Franco, F.G., Roveda, F., de Matos, L.N., Braga, A.M., Rondon, M.U., Rotta, D.R., Brum, P.C., Barretto, A.C., Middlekauff, H.R., Negrao, C.E., 2007. Exercise training reduces sympathetic nerve activity in heart failure patients treated with carvedilol. Eur. J. Heart Fail. 9, 630–636. Gademan, M.G., Sun, Y., Han, L., Valk, V.J., Schalij, M.J., van Exel, H.J., Lucas, C.M., Maan, A.C., Verwey, H.F., van de Vooren, H., Pinna, G.D., Maestri, R., La Rovere, M.T., van der Wall, E.E., Swenne, C.A., 2011. Rehabilitation: periodic somatosensory stimulation increases arterial baroreflex sensitivity in chronic heart failure patients. Int. J. Cardiol. 152, 237–241. Guidelines, H., 1996. Heart rate variability. Standards of measurement, physiological interpretation, and clinical use. Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. Circulation 93, 1043–1065. Hammond, R.L., Augustyniak, R.A., Rossi, N.F., Churchill, P.C., Lapanowski, K., O'Leary, D.S., 2000. Heart failure alters the strength and mechanisms of the muscle metaboreflex. Am. J. Physiol. Heart Circ. Physiol. 278, H818–H828.

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